Question

You are conducting an experiment inside a train car that may move along level rail tracks. A load is hung from the ceiling on a string The load is not swinging. and the string is observed to make a constant angle of 45 degree with the horizontal. No other forces are acting on the load. Which of the following statements are correct?
A) The train is an inertial frame of reference
B) The train is not an inertial frame of reference
C) The train may be instantaneously at rest
D) The train may be moving at a constant speed in a straight line
E) The train may be moving at a constant speed in a circle
F) The train must be speeding up
G) The train must be slowing down
H) The train must be accelerating

Answer 1

Answer:

B) The train is not an inertial frame of reference

C) The train may be instantaneously at rest

D) The train may be moving at a constant speed in a circle

H) The train must be accelerating.

Explanation:

Since the train is in constant motion, it is accelerating. The speed is varying with time. The train is not an inertial frame of reference since it is constantly moving.

Answer 2

Answer:

The train is not an inertial frame of reference

The train may be instantaneously at rest

The train may be moving at a constant peed in a circle

The train must be accelerating.

Explanation:

The train is not an inertial frame of reference because the string makes an angle of 45 degrees with the horizontal and vertical, and hence the force acting upon it is not zero.

The train may be instantaneously at rest which does not imply that the velocity of the train is zero, but at a particular time t, the velocity is zero.

Since we have ascertained that the acceleration is not 0, and it is not an inertial frame of reference, it means that the train is in accelerating condition and hence it is possible that the train may be moving at a constant peed in a circle

In the case of the train, one thing that has been established is that, while the velocity of the train might be 0, the train is in accelerating condition and hence "the train must be accelerating" is a correct statement.